Pilot studies performed by us for this proposal have resulted in the successful treatment of viral-leukemia in a significant number of animals of a mouse-model through adoptive-immunotherapy involving marrow transplantation from histoincompatible donors. In these studies the native leukemia-resistance of the donor tissue was considered paramount to any graft-vs-host (GvH) reaction which might occur as a result of the selection of donor tissue. An interesting, but unexpected, finding resulting from this was that no severe GvH response was found in the leukemic recipients, while a lethal GvH reaction occurred in the engrafted normal controls. The proposed studies aim to further improve survival and answer some of the questions posed by the pilot study. This will be approached through: 1) Determining the optimal marrow ablating preparatory treatment of the leukemic transplantation recipients used in the model, 2) Varying of the host/donor combinations used for leukemia induction and marrow transplantation therapy to expand the base of the model in order to improve our understanding of the histocompatibility influences and other immunogenetic factors involved in the native leukemia resistance of the donor tissue, and, 3) Introduction of definitive immunobiological tests to increase our knowledge of the events involved in the occurrence or non-occurrence of GvH response, the development of allogeneic-tolerance in the engrafted viral-leukemic host, and the lack of development of this tolerance in normal hosts grafted with the same histoincompatible marrow cell preparation.